Multi-story reinforced concrete buildings recently built and currently being built in the United States follow one or the other of two different construction systems which both adhere, one more than the other, to a common design philosophy. One construction system is that of the poured-in-place ductile frame building where all steel reinforcing bars or rods (rebar) are placed in forms erected at the building site and concrete is poured into the forms around the rebar elements. Ductile frame buildings are substantially the structural equivalent, in reinforced concrete, of steel frame buildings. The other construction system uses precast reinforced concrete building components which are tied or knit together at the building site to provide a structure of the requisite lateral stability. For buildings of comparable height and size, reinforced concrete buildings built according to the ductile frame system cost from 10 to 15 percent more to erect than buildings using the precast component system. Despite the cost premiums, ductile frame systems are used in the construction of multi-story office buildings more frequently than precast component systems are used. Precast component systems are used frequently to build parking structures and the like, rather than office buildings.
The present design philosophy followed in the United States for precast concrete buildings, and for cast-in-place buildings, is to provide the requisite lateral stability for the building in massive shear walls and/or ductile frame to which all other parts of the building are tied in a secure manner. The shear walls may be windowless end walls of the building in combination with a substantially continuous diaphragm wall in the building at right angles to the end shear walls; such arrangements are often found in parking structures and other buildings, not office buildings, where windows are not specially desired. An alternate form of the same philosophy is the use of internal shear walls, at right angles to each other, which have limited penetrations, such as doorways, through them. Such main shear walls are relied upon to keep the building stable and erect when the building experiences loads such as those imposed by wind or seismic events, for example. This design philosophy is unattractive for use in designing multi-story office buildings or other buildings where substantial window area in all exterior walls is desired, and where open interior space is desired for flexible and economic usage of floor area and for efficient traffic flow. Nevertheless, multistory reinforced concrete office buildings, as high as 20 stories are known; they most commonly are of the poured-in-place ductile frame kind.
Further, present design approaches to precast concrete buildings do not well use precast concrete components because they cannot economically be tied together and to the shear walls. Presently, such components must either be welded to the shear walls or be knit to the shear walls by pouring concrete on the site into forms around rebars extending from the shear walls and from the adjacent precast components. Extensive use of on-site welding, or of on-site pouring, or both, detracts from the economics of off-site manufacture of precast concrete components.
The necessary lateral stability for precast concrete buildings can be obtained by reliance upon exterior wall panels which afford substantial window area and which extend between adjacent exterior columns of the building, provided that the connections of the wall panels to the columns can transmit lateral loads. Poured-in-place floor diaphragms can be provided with minimal use of forms to tie precast girders, beams and floor panels together and to the exterior wall panels to satisfy remaining requirements for building lateral stability. The important criterion is that the connections of the precast wall panels to the precast columns be adequate to carry loads of the magnitudes associated with design wind, seismic and other loads. Adequate connection integrity and capacity could be provided by use of welded or poured-in-place connections, each of which is expensive and, as noted, detracts from the manufacturing and installation economics associated with precast concrete components.
It is seen, therefore, that a need exists for a way to efficiently, effectively and economically connect precast reinforced concrete wall panels to columns in a reinforced concrete building with minimum use, preferably no use, of welding or of on-site pouring of concrete. Satisfaction of that need will enable the economic and safe erection of multi-story office buildings and the like having substantial window area in all exterior walls and having substantially open and uninterrupted floor spaces.